1. Field of the Invention
This invention relates to apparatus, commonly referred to as retrievers, used in removing and installing plungers in the well head of a hydrocarbon producing well. More specifically the invention relates to such apparatus that employ a magnetic latching mechanism for engaging the plunger in both removing the plunger from a well and replacing a plunger in a well.
2. State of the Art
A plunger lift is an apparatus that is used commonly in the oil and gas industry to increase the productivity of oil and gas wells. Descriptions of the use of such plunger lifts are well described in the following U.S. Pat. Nos. 2,661,024; 6,719,060; 6,935,427; and 7,383,878. As explained in these patents, a plunger is designed to intermittently drop to the bottom of a well and then rise to the top carrying well liquids out of the well that would otherwise collect at the bottom of the well and thus decrease the efficiency of the operation of the well.
When the plunger rises to the top of the well it is retained in a receiver near the well head until it is to be dropped back down the well. The receiver is also commonly called a lubricator. The plunger requires recurrent maintenance and periodic replacement which requires that the plunger be repeatedly removed from the receiver or lubricator. This is done by taking a cap off the well head and using a retriever apparatus to reach down into the receiver or lubricator and retrieve the plunger through the open end of the well head.
Retrievers have been used that employ different mechanical means to attach to the upper end of the plunger in able to pull the plunger up and out of the well head. These mechanical connectors often employ collets, fingers or other projections that catch an engagement means on the upper end of the plunger. The retrievers are carried from well to well in the back of a truck of the person servicing the well, and the collets, fingers or other projections are subject to being broken and bent to where they are unusable. Further dirt and grime can accumulate in the fingers and projections again rendering them inoperable at least until they are thoroughly cleaned.
A retriever has been used that employs a magnetic connection between the distal end of the retriever and the plunger. In FIG. 1 there is shown a longitudinal cross-sectional view through such a retriever that is currently being used and which uses a magnetic connection with the plunger. As shown in FIG. 1, the prior art retriever comprises an elongate, solid handle 10 that is cylindrical in shape, i.e., has a round transverse cross-section. The handle 10 is made of aluminum. A block 11 of polymeric material such as polyethylene is press fit onto the distal end of the handle 10. A bore 12 is formed inwardly from the distal end of the block 11, and a magnet 13 is received in that bore 12. The magnet 13 is itself press fit into a brass ring 14, which in turn is press fit into a steel ring 15, with the assembled magnet 13, and rings 14 and 15 being press fit as a unit into the bore 12 of the block 11 at the distal end of the handle 10. A series of grooves 16 are formed near the proximal end of the handle 10 as means for firmly grasping the handle 10.
In the device of the prior art as shown in FIG. 1, the face 18 of the magnet 13 is exposed and subject to being impacted at its exposed face by other tools and so forth as it is being transported in the bed of a truck from one well to another. The magnet 13 is very brittle and subject to being broken by such impacts on the exposed face 18 of the magnet 13. To minimize impact of the magnet 13 with the plunger when the retriever is being used, the block 11 is provided with a circular, projecting lip 17 from the face 18 of the magnet 13 at the perimeter of the block 11.
In use, that lip 17 can be worn away or broken away which can result in the plunger impacting the magnet 13 when the retriever is lowered into the well head to retrieve the plunger. Again, the magnet 13 is very brittle and it is imperative that the magnet 13 is not chipped or broken such that pieces of the magnet 13 get dropped into the well. Thus, care must be exercised to insure that there has been no damage to the lip 17 whenever the retriever is used.
When the lip 17 is in proper, undamaged condition, the stand-off space created between the plunger and the magnet 13 by the lip 17 decreases the lifting power of the retriever. Another problem associated with the existing magnet retriever is its inability to readily let go of the plunger when inserting the plunger through the well head into the receiver of the well. The magnetic retriever of the prior art as shown in FIG. 1 has to be vigorously shaken to disengage the plunger from the magnetic connection. That risks damaging the plunger and the receiver or lubricator of the well when the plunger drops when it breaks magnetic connection to the retriever.